Technical Field
This invention relates to artificial intervertebral joints. In particular, the invention relates to artificial implantable intervertebral disc joints with controls for adjustable positioning of surfaces related to load-bearing and force-distribution.
State of the Art
The spinal column is a segmental chain of vertebrae. Each vertebra comprises an anterior, roughly cylindrical vertebral body and posterior elements forming bony canal surrounding the spinal cord and spinal nerve roots. The posterior bony canal components of each vertebra articulate with adjoining vertebra above and below at facet joints forming a load-bearing structure known as the posterior column. The anterior vertebral bodies, in turn, articulate at intervertebral disc joints collectively forming the load-bearing structure known as the anterior column. In humans and other animals, axial loads are distributed between the anterior and posterior columns. Motion at the facet joints affects load distribution forces in both columns and, similarly, motion at the intervertebral disc joints also affects load distribution forces in both columns.
The human intervertebral disc (“IVD”) is a soft-tissue structure sandwiched between the bony end-plates of the vertebral body above (cranial) and the vertebral body below (caudal). This soft-tissue disc comprises a fibrous ring-shaped wall of tissue (anulusus fibrosis) surrounding a gelatinous core (nucleus pulposis.) The natural IVD space allow for motion in the anterior-posterior plane, such as flexion and extension; lateral motion to either side, and axial rotation. The human IVD joint has a non-fixed, mobile center of rotation (“COR”), or collection of multiple CORs otherwise known as a centrode, about which axial rotation occurs.
The IVD joint is vulnerable to a variety of degenerative processes, of both traumatic and non-traumatic etiologies, which are sometimes treated by surgically replacing the IVD joint with a prosthetic device. Available prosthetic devices, however, are limited in capacity to reproduce the natural load-bearing mechanics and range of motion of the native IVD joint.
Accordingly, what is needed is a device that provides a structure and mechanism of reproducing a more natural range of motion of an IVD joint.